PORTLAND, Maine (AP) — The new guns on the Navy's biggest and most advanced destroyer are going to be firing blanks if the Navy can't find cost-effective projectiles.

The GPS-guided, rocket-powered projectiles developed for the new 155mm Advanced Gun System currently cost about $800,000 apiece, nearly as much as a cruise missile, making them too expensive for the Navy to buy in large quantities for the stealthy USS Zumwalt, according to officials.

The projectiles were supposed to be less expensive than missiles, providing a cost-effective way to pummel targets from 70 miles away, clearing a path for amphibious landings.

But the current price compares with $1 million for a cruise missile, which has a range of 1,000 miles. And the price is expected to grow, officials said.

For now, there are no plans to buy projectiles beyond the initial purchase of 90, according to the Navy's draft 2018 budget. The Zumwalt is supposed to be stocked with 600.

It's stunning news for a program plagued by growing costs.

"Congress is going to want to know how the Navy could get so far down the road without realizing that the price tag on these projectiles is so high," said Loren Thompson, defense analyst at the Lexington Institute in Arlington, Virginia.

The Navy is evaluating alternatives for ammunition for the Zumwalt and two other ships in the class that are under construction at Bath Iron Works in Maine. Those options include both conventional and hyper-velocity projectiles, said Navy Capt. Thurraya Kent.

Bethesda, Maryland-based Lockheed Martin, which developed the 155mm projectiles, blamed the low production rate of ships — only three are being built, compared with the 32 originally envisioned — for driving up costs of the guided munitions. The defense contractor is working with the Navy with options, a spokeswoman said.

The Navy has been struggling to reduce costs because of budget limits, but those constraints could be eased when Republican President-elect Donald Trump takes office. He has vowed to boost defense spending and to increase the size of the U.S. fleet.

The 610-foot Zumwalt, the first ship in the class, was commissioned into service last month and is currently en route to its home port in San Diego.

The destroyer features electric propulsion, an angular shape to minimize radar signature, an unconventional wave-piercing hull, and a deckhouse that hides radar and other sensors. The 155mm Advanced Gun System was designed by BAE Armament Systems.

The ships weigh in at nearly 15,000 tons, about 50 percent heavier than current destroyers. But the crew size is half of the 300 personnel of other destroyers, thanks to automation.